Antibiotic resistance is an increasing public health problem that is associated with considerable morbidity, mortality and costs. Given the reduced pace of antibiotic discovery and the approaching demographic shift towards an increasingly aged population, antibiotic resistance among the geriatric population in both hospitals and long-term care facilities (LTCFs) represents an impending public health disaster. My long-term career goal is to help reduce the incidence of antibiotic-resistant infections in both hospitals and LTCFs. The purpose of this application is to provide me with opportunities for specific training in geriatric medicine, mathematical modeling, and infectious diseases to assist in my development into an infectious disease epidemiologist with expertise in geriatric medicine. This research plan is designed to provide these opportunities and will use a multi-disciplinary approach to assess three hypotheses related to colonization by methicillin-resistant Staphylococcus aureus (MRSA) in hospitals and LTCFs. MRSA is one of the most common antibiotic-resistant bacteria and a prevalent nosocomial pathogen. Appropriate understanding and quantification of the association between antibiotic use, patient movement, and colonization of patients with MRSA are necessary in order to optimize existing infection control efforts and to identify additional opportunities for control of these pathogens. Thus, my long- term goal and the goals of this project are consistent with the mission of NlAID in attempting to understand and ultimately prevent infectious diseases that threaten millions of human lives. The proposed study will utilize admission and biannual point prevalence studies at four LTCFs over two years, a prospective cohort of LTCF residents to assess both the prevalence of MRSA upon admission to acute care hospitals and outcomes associated with colonization by MRSA, and mathematical models to assess relative contributions of inter-facility patient movement on MRSA prevalence as well as the effectiveness and cost-effectiveness of infection control interventions targeting recently transferred patients in reducing the transmission of MRSA. These data are integral to the prevention of infections by MRSA and potentially other antibiotic-resistant bacteria.